Hydrometallurgy involves the reduction of ores and minerals by washing out insoluble matter with various liquids.
The great majority of copper produced in the world today is recovered from sulfide ores and concentrates by smelting processes. These smelting processes suffer from the fact that large quantities of sulfur dioxide are produced. Unless controlled, the sulfur dioxide poses a serious threat to the environment due to its toxic and poisonous nature. Thus, smelting processes have found it necessary to abate the expulsion of such gases into the atmosphere. However, current methods for removal of sulfur dioxide from stack gases are generally found to be uneconomical because the products which may be derived from the gas (sulfuric acid, sulfurous acid, or sodium sulfite) are generally produced at too great a distance from market areas to justify shipping costs. As a result, most process gases remain untreated and are discarded into the atmosphere creating severe environmental pollution problems.
Hydrometallurgical processes have been developed in order to overcome the problem of sulfur dioxide emissions. Unfortunately, none of these processes appear commercially practicable at the present time. Horton, in his U.S. Pat. No. 2,970,096, developed a means for treating oxidized copper ores. Such ores were leached with an alkaline leach solution while scrubbing the ore particles to remove the silica gel therefrom. Horton's process found particular use in connection with oxidized copper ores which contain calcium and/or magnesium carbonates.
Another means for recovering copper has been by use of ammonia systems. However, such processes present serious problems in the recovery and recycling of ammonia. The use of acid systems for oxidative leaching are effective only under conditions of temperature and pressure that yield excessive corrosion of equipment.
Accordingly, it is an object of our invention to provide a method whereby copper may be recovered from sulfide ores in both an economic and pollution free manner.
It is a further object of our invention to provide a means for reducing atmospheric pollution by development of a nonsmelting method of copper production.